1. Field of the Invention
The present invention relates to an apparatus for detecting a connection state between an earphone plug and a corresponding jack of a mobile communication terminal, and more particularly to an apparatus for detecting a connection state between a stereo earphone plug and a corresponding jack of a mobile communication terminal.
2. Description of the Related Art
Various methods for detecting a connection state between an earphone plug and a corresponding jack of a GSM mobile terminal are well known in the art. However, with the development of audio/video technology, the need for reproducing moving images has been rapidly increasing in recent times. Thus, stereo reproduction needs to be readily performed by such a mobile communication terminal.
FIG. 1 illustrates a block diagram of a general mobile communication terminal. Referring to FIG. 1, a mobile communication terminal includes a RF (Radio Frequency) signal processor 100, an IF (Intermediate Frequency) signal processor 102, a controller 104, a storage unit 106, a display 108, an input unit 110, and a voice processor 112, which is connected to a microphone and speaker. An apparatus for detecting a connection state between an earphone plug and a corresponding jack of a mobile communication terminal is positioned in the voice processor 112. The voice processor 112 transmits a signal for indicating a connection state between the earphone plug and the corresponding jack to the controller 104. The controller 104 outputs an acoustic signal to an earphone according to the signal received from the voice processor 112.
FIG. 2 illustrates a schematic diagram of a conventional apparatus for detecting a connection state between an earphone plug and a corresponding jack 200 of a mobile communication terminal. Referring to FIG. 2, the apparatus shifts a level of a signal entered into the controller 104 using a microphone bias and a comparator 210 in order to determine whether an earphone plug is connected to a corresponding jack of a mobile communication terminal. But, this method has a disadvantage in that it is available for only a mono signal. In other words, the above method is applicable to a mobile communication terminal whereby a voltage difference exists between an output voltage of a microphone's positive terminal (+) and the other output voltage of a microphone's negative terminal (−). Earphone jacks can be divided into a mono type as shown in FIG. 2 and a stereo type as shown in FIG. 3. Table 1, below, shows the terminal layouts of conventional mono and stereo earphone jacks corresponding to conventional mono and stereo earphone plugs, respectively.
TABLE 1MONOSTEREOTerminal 1MIC−SPEAKER-LEFTTerminal 2MIC+MICTerminal 3Plug InsertingPlug InsertingDetectionDetectionTerminal 4XXTerminal 5SPEAKERSPEAKER-RIGHTTerminal 6GROUNDGROUND
As shown in Table 1, a mono earphone jack has polarized terminals MIC+ (positive terminal) and MIC− (negative terminal), which create the voltage difference that the conventional apparatus uses to detect a connection state of a mono earphone plug. However, the stereo earphone jack has only an unpolarized MIC terminal. Therefore, if a user wants to implement a stereo mode in his or her mobile communication terminal, it is impossible for the above method to detect a connection state between a stereo earphone plug and a corresponding jack of such a mobile communication terminal because a stereo audio signal is a one side ended signal.